There have conventionally been proposed various seatbelt retractors which remove slack of webbing in case of an emergency such as vehicle collision or the like.
For instance, in the seatbelt retractor as disclosed in Japanese Patent Application Laid-open Publication No. 2009-241863, a pretensioner unit is constituted of a pretensioner mechanism and a forced locking mechanism. In case of vehicle collision, the forced locking mechanism is actuated approximately at the same time as the pretensioner mechanism starts operating, and after a webbing is taken up by the pretensioner mechanism, it locks pull-out of the webbing to prevent a drop in belt load when passengers move towards the front of the vehicle. The forced locking mechanism is arranged inside a base block body constituting the pretensioner mechanism.
The base block body has a concave portion formed therein for accommodating the forced locking mechanism which in turn is constituted of a push block, a rotating lever, a block urging spring for urging the push block in the direction of the rotating lever side, a gear-side arm and an urging spring for urging the gear-side arm in the direction of the rotating lever side. A coupling shaft and a mechanical arm constituting the forced locking mechanism are connected to this gear-side arm from the outer side of a base plate.
When a gas generating member of the pretensioner mechanism is actuated in case of vehicle collision, a piston inside a pipe cylinder moves upwards from its normal condition, causing a pinion gear body to rotate. As a result, teeth of a pinion gear portion come in contact with the push block and force it towards outside. In turn, the push block is further forced by the block urging spring causing the rotating lever to rotate which disengages a lower end portion of the rotating lever from a front end portion of the gear-side arm. With this configuration, the gear-side arm is rotated towards the outside by the urging spring, the mechanical arm rotates via the coupling shaft, causing a pawl which is rotatably supported on a side wall portion of a housing unit to rotate and engage a ratchet gear of a take-up drum unit.
Nevertheless, the seatbelt retractor described in the above-mentioned Japanese Patent Application Laid-open Publication No. 2009-241863 employs the block urging spring for urging the push block in the rotating lever-side direction and the urging spring for urging the gear-side arm in the rotating lever-side direction. The respective springs are configured so as to be held, in normal state before the pretensioner mechanism starts operating, inside the push block in a state allowing for urging force to be generated when the forced locking mechanism is in operation. Thus, the push block is required to have the strength to hold this urging force. This makes it difficult to achieve a compact design and a lightweight device, etc.